1. Field of the Invention
This invention relates to air break disconnecting switches and more particularly to a double side air break disconnecting switch wherein an elongated switchblade is connected to a rotatable center insulator for rotation therewith and has rigidly secured to its outer ends a jaw type contact which engages contact bars mounted on the outer insulators.
2. Description of the Prior Art
The most commonly used double side air break disconnect switch is a low profile, group operated, three insulator air break disconnecting switch, in which the center insulator is rotated to open and close the switch. U.S. Pat. Nos. 2,760,019; 3,134,865; and 3,836,737 are exemplary of various types of the most common horizontal double air break disconnecting switch. These patents illustrate various kinds of horizontal double break disconnecting switches wherein the jaw contacts are supported on stationary insulators and the switchblade is rotated about its longitudinal axis to make high pressure electrical contact between the blade jaw contacts.
In a conventional double side break air disconnect switch rotation of the center insulator rotates an elongated switchblade about its vertical axis, which is perpendicular to its longitudinal axis, into the jaw contacts. When the blade tips reach a stop inside of the jaw contacts, further rotation of the center insulator will cause the blade to roll over around its longitudinal axes to establish high pressure electrical contact.
One problem with this type of a prior art air break disconnect switch construction is that if the blade hits an obstacle, such as an ice buildup, before it has entered the jaw contacts, it will rotate about its longitudinal axis prematurely. Another problem is sometimes encountered if the switch is operated at a high speed, during the closing sequence the blade can prematurely rotate and come in flat, the fully closed position, against the jaw contacts. During fast closing, the switchblade can also bounce out of the jaw contacts and twist to a fully closed position outside the contact shoes. Little or no contact pressure can be established if these undesirable events occur. These events can sometimes occur, however, since the switchblade is not fully controlled at all times.
U.S. Pat. No. 1,792,282 to H. J. Crabbs et al. and U.S. Pat. No. 1,901,688 to A. Alsaker et al. illustrate air break disconnecting switches wherein a jaw contact is carried by a movable switchblade. The Crabbs et al. patent illustrates a single disconnect switch wherein the switchblade is rotated about its longitudinal axes to cause high pressure engagement with a stationary contact bar. The switchblade in Crabbs et al. when moving from a closed position is pivoted to disengage from the stationary contact and moves to a partially upright open position. In Alsaker et al. a horizontal side double break air disconnect switch is disclosed wherein all three insulating stacks are movable. The jaw contacts are positioned to engage a vertical contact bar. The center insulator stack is rotated to bring the jaw contacts supported on the ends of the switchblade around the vertical contact bars. The outside insulators which support the vertical contact bars are then rotated to cause high pressure engagement between the contact bars and the associated jaw contacts.
U.S. Pat. No. 2,306,117 to J. P. Dunlap shows an air break disconnect switch wherein a jaw type contact is supported for pivotal movement from a stationary insulator stack. FIGS. 8 and 9 of Dunlap show this concept as applied to a double break horizontal disconnecting switch. The jaw type contacts are supported from each end stationary insulator for movement in a horizontal plane. U.S. Pat. No. 2,707,732 to T. B. Ortwig shows another high voltage air disconnect switch wherein a jaw contact is pivotally supported from a stationary insulator.
U.S. Pat. No. 2,293,652 to T. F. Johnson illustrates a single break air disconnecting switch wherein a contact bar is supported for pivotal movement on a stationary insulator stack. During operation the double switchblade portions move generally along their longitudinal axis to engage the pivotable contact bar.
In constructing a double break disconnecting switch it is desirable if the switchblade is always fully controlled. It is also desirable that the switch be relatively simple, inexpensive, and easy to maintain. A further desirable feature for a competitive air break disconnect switch is that it be operable by a relatively low torque.